1. Field of the Invention
The present invention relates generally to a diffractive light modulator and, more particularly, to a diffractive light modulator, which reflects and diffracts incident light depending on the height difference between neighboring cantilevers that are constructed in such a way that the first ends thereof are supported by one or more support units and the second ends thereof are free.
2. Description of the Related Art
Generally, an optical signal processing technology has advantages in that a great amount of data is quickly processed in a parallel manner unlike a conventional digital information processing technology in which it is impossible to process a great amount of data in real time. Studies have been conducted on the design and production of a binary phase filter, an optical logic gate, a light amplifier, an image processing technique, an optical device, and a light modulator using a spatial light modulation theory.
The spatial light modulator is applied to optical memory, optical display device, printer, optical interconnection and hologram fields, and studies have been conducted to develop a display device employing it.
The spatial light modulator is embodied by a reflective deformable grating light modulator 10 as shown in FIG. 1. The modulator 10 is disclosed in U.S. Pat. No. 5,311,360 by Bloom et al. The modulator 10 includes a plurality of reflective deformable ribbons 18, which have reflective surface parts, are suspended on an upper part of a silicon substrate 16, and are spaced apart from each other at regular intervals. An insulating layer 11 is deposited on the silicon substrate 16. Subsequently, a sacrificial silicon dioxide film 12 and a low-stress silicon nitride film 14 are deposited.
The nitride film 14 is patterned by the ribbons 18, and a portion of the silicon dioxide film 12 is etched, thereby maintaining the ribbons 18 on the oxide spacer layer 12 by a nitride frame 20.
In order to modulate light having a single wavelength of λ, the modulator is designed so that thicknesses of the ribbons 18 and oxide spacer 12 are each λ/4.
Limited by a vertical distance (d) between a reflective surface 22 of each ribbon 18 and a reflective surface of the substrate 16, a grating amplitude of the modulator 10 is controlled by applying voltage between the ribbon 18 (the reflective surface 22 of the ribbon 18 acting as a first electrode) and the substrate 16 (a conductive layer 24 formed on a lower side of the substrate 16 to act as a second electrode).
In an undeformed state of the light modulator with no voltage application, the grating amplitude is λ/2 while a total round-trip path difference between light beams reflected from the ribbon and substrate is λ. Thus, a phase of reflected light is reinforced.
Accordingly, in the undeformed state, the modulator 10 acts as a plane mirror when it reflects incident light. In FIG. 2, the reference numeral 20 denotes the incident light reflected by the modulator 10 in the undeformed state.
When proper voltage is applied between the ribbon 18 and substrate 16, the electrostatic force enables the ribbon 18 to move downward toward the surface of the substrate 16. At this time, the grating amplitude is changed to λ/4. The total round-trip path difference is a half of a wavelength, and light reflected from the deformed ribbon 18 and light reflected from the substrate 16 are subjected to destructive interference.
The modulator diffracts incident light 26 using the interference. In FIG. 3, reference numerals 28 and 30 denote light beams diffracted in +/−diffractive modes (D+1, D−1) in the deformed state, respectively.
However, the above-described conventional light modulator must displace the ribbons in a vertical direction to diffract incident light, so that the conventional light modulator is disadvantageous in that bending is formed on the portions of the ribbons that reflect and diffract the incident light, thus deteriorating the characteristics of reflected and diffracted light.
Furthermore, the conventional light modulator is problematic in that high actuating voltage is not only required, but the actuating speed thereof is also slow because the conventional modulator must displace the ribbons in a vertical direction to reflect and diffract incident light.
Furthermore, the ribbons of the conventional modulator must be manufactured to have a thickness of about 0.5 μm, so that it is difficult to perform a process of manufacturing the conventional modulator. Accordingly, the conventional light modulator is problematic in that it is difficult to achieve the mass production of light modulators that are accurately operated.